As is known, belts made of elastomeric material intended to be assembled around at least two pulleys and to exchange, on appropriate surfaces, friction forces able to transmit motion, comprise substantially a ring-shaped body which has embedded therein in a same plane a plurality of tension-resistant elongated elements whose main feature is their inextensibility.
The belt body is internally and externally limited by a pair of base surfaces and, laterally, by a pair of opposite sides.
Belts of the above type can have an V-shaped section and can transmit the friction forces by their sides, or a flat section and transmit the friction forces by at least one of their bases. Alternatively, they can be of the Poly-V type, identified in cross section by a base surface comprising several V-shaped longitudinal grooves arranged side-by-side.
These belts find application in many fields, and in particular they are mainly used for power drives in which one of the pulleys can have very small take-up diameters, in some cases 70 mm, and often even smaller, ranging between 40 and 50 mm. Moreover, the present technical trend is to use the above belts on pulleys having diameters of 15 or 16 mm.
Unfortunately, the application of the belt on a pulley having a high curvature may lead to a reduction in the belt life.
In fact, considering for instance a Poly-V belt mounted on the corresponding pulley, it can be noted--as known to the technicians of this field--that the stresses are distributed on the two parts of the annular body, i.e. above and below the surface containing the elongated elements; more precisely, the belt portion above these elements is subjected to tension, while that below them is subjected to compression. At said surface containing the reinforcing elements, due to the inextensibility of the reinforcing elements, no deformations occur and said surface can be defined as a "neutral axis," or "pitch surface," of the belt.
The compression of the considered belt portion is greater the greater the pulley curvature, with a consequent high deformation of the elastomeric material which may give rise to substantially undulated configurations in areas corresponding to the joint between the longitudinal elements and the annular elastomeric body.
It has been noted that such deformations may originate sooner or later--but in any event in times not permissible for the services required in many industrial applications--resulting in detachment of the elongated elements forming the elastomeric body, with a consequently reduced life of the belt.
The drawbacks ascertained in the Poly-V belts are common to other types of V-shaped or flat belts and can be ascribed also here to the compression of the belt portion underlying the "pitch surface" containing the longitudinal elements and to a "collapse" of the elastomeric material, compelled to deform and to find space to enable said deformation where this is possible, inter alia, towards the elongated elements, with the already known consequences.